Electrical bushing with spaced conductor with metallic powder for thermally connecting the bushing and conductor



Apnl 16, 1963 I. ,s. GARD 3,086,075

ELECTRICAL BUSHING WITH SPACED CONDUCTOR WITH METALLIC POWDER FORTHERMALLY CONNECTING THE BUSHING AND CONDUCTOR Filed March 1, 1960INVENTOR. //VG J. cffleg A Tram W575 nited States atent 3,086,075ELECTRICAL BUSHING WITH SPACED CONDUC- TOR WITH METALLIC POWDER FORTHER- MALLY CONNECTING THE BUSHING AND CONDUCTOR Inge S. Gard, Ludvika,Sweden, assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa.Filed Mar. 1, 1960, Ser. No. 12,075 Claims priority, application SwedenMar. 5, 1959 4 Claims. (Cl. 174152) This invention relates to anelectrical bushing insulator of the type wherein an electrical conductormay be carried through some type of metallic housing in insulatedrelation with respect to the housing and more specifically relates to anelectrical bushing insulator wherein the space between the outerdiameter of the central conductor and the inner diameter of the outerinsulator housing is filled with a compressible medium of relativelyhigh thermal conductivity with respect to air.

In the past electrical bushing insulators have been formed of a tube ofceramic material such as porcelain, and these tubes receive a centralconductor therethrough. The outer porcelain tube is then provided with asecuring means so that the complete assembly of insulator and centralconductor may be connected to a support structure which will beinsulated with respect to the central conductor. Since the centralconductor within the outer insulator housing will have a coetficient ofthermal expansion substantially different from that of the insulator, itis normally necessary to provide space between the outer diameter of thecentral conductor and the inner diameter of the insulator housing sothat the conductor may expand and contract responsive to temperaturefluctuation without causing a fracture of the insulator housing. Notethat the temperature change to which the assembly may be exposed can beof appreciable magnitudes as where the bushing assembly is used in theoil tank of an oil interrupter and is exposed to the hot ionizationproducts of interruption when the oil circuit interrupter is operated toa circuit open position.

In view of this required spacing, there will be a cushion of air whichsurrounds the central conductor where this layer of air interferes withefiective cooling of the central conductor. The problem of cooling thecentral conductor is made worse since the circuit terminal which mayhave a relatively high resistance will be immediately adjacent the ofend of this conductor so that a substantial amount of heat is generatedin the central conductor and cannot be effectively removed to the outerinsulator housing.

The principle of the present invention is to fill the aforementioned airspace surrounding the central conductive member with a compressiblemedium having a relatively high thermal conductivity with respect to thethermal conductivity of air. By way of example, this space may be filledwith copper filings or a powdered conductive material. By using apowder, the central conductor is still free to expand withouttransmitting substantial stress to the outer housing and at the sametime the thermal conductivity of the powder will permit a conductiveflow of heat from the central conductor to the housing. By way ofexample, since the heat is moved in this highly efiicient manner, thecurrent conducting capacity of the bushing insulator may besubstantially doubled for the same cross-sectional area of the centralconductor.

Further advantages flow from this novel structure whereby it is nolonger necessary to coat the inner surface of the insulator housing witha conductive material such as graphite in order to avoid corona betweenthe conductor and the housing wall. That is to say, since thecompressible medium is electrically conductive, the graphiting processmay be eliminated. While the thermally conductive medium can be of anytype of material, it is preferably of a nonmagnetic material in the caseof an A.-C. bushing insulator to avoid heat generated by eddy currentlosses in the medium.

Accordingly, the primary object of this invention is to provide a novelelectrical bushing insulator.

Another object of this invention is to provide a novel electricalbushing insulator having an increased current rating.

A further object of this invention is to provide a novel electricalbushing insulator wherein the central electrical conductor is thermallyconnected to its outer insulator housing through a relativelycompressible medium having a relatively high thermal conductivity withrespect to air.

A still further object of this invention is to fill the space betweenthe central conductor and outer insulator housing of an electricalbushing insulator with a compressible medium having a relatively highthermal conductivity with respect to the thermal conductivity of air.

A further object of this invention is to replace the coating of theinner surface of the insulator housing of an electrical bushinginsulator by filling the space between the insulator and its centralconductor with a medium of relatively high conductivity with respect toair.

These and other objects of the invention will become apparent from thefollowing description when taken in connection with the drawing whichshows an electrical insulator bushing of the typical type wherein anouter insulator housing 1 which may be of porcelain or any other desiredinsulator material has an external flange 2 fastened thereto in anydesired manner. The insulator housing 1 can be secured to flange 2, forexample, in the manner shown in copending application Serial No.853,185, filed November 16, 1959, now Patent 3,011,013, entitled Methodfor Joining Two Tubular Parts.

The central conductor 3 is carried centrally of the central openingwithin insulator housing 1 and may be of copper or any other desiredmaterial. More specifically, central conductor 3 may be held by means ofthe two clamping conductor members or support means 3a and 3b which aresecured to conductor 3 in any desired manner and clamped into respectiveends of insulator housing 1 as shown. Conductor 3 is then terminated ateither end by terminal members 4 and 5 which can be of any standardconstruction.

The insulator described up to this point is typical of presentcommercially used electrical bushing insulators, and it will be notedthat the external diameter of conductor 3 is less than the internaldiameter of bushing insulator 1. This spacing is provided purposelybecause of the diiferent thermal coefficients of expansion of insulator1 and conductor 3 and prevents the transmission of stress to insulator 1under high temperature change conditions. This space, however, providesa thermal barrier where the space is filled with air so that the heat isnit efficiently conducted from conductor 3 to insulator In accordancewith the present invention, the space between the conductor and housingis filled with a medium 6 of relatively good thermal conductivity withrespect to the thermal conductivity of air. By way of example, medium 6may be formed of a copper powder. With this novel medium 6 of relativelygood thermal conductivity, it will be apparent that heat may betransmitted from conductor 3 to insulator 1 by conduction, whereby ithas been found that the current carrying capacity of conductor 3 for thesame size conductor and same temperature rise can be doubled withrespect to the use of the conductor with a surrounding air space.

Furthermore, since the relatively good thermally conductive medium 6will also be electrically conductive, the inner surface of insulator llneed not be coated with a conductive material such as graphite tocontrol corona effects.

Although preferred embodiments of the novel invention have beendescribed, many variations and modifications will now be obvious tothose skilled in the art, and it is preferred, therefore, to be limitednot by the specific disclosure herein but only by the appended claims.

What is claimed is:

1. An electrical bushing insulator; said electrical bushing insulatorcomprising an outer insulator housing having a central opening therein,a conductor passing through said opening and extending beyond either endof said outer insulator housing and a support means; said support meansbeing connected between said insulator housing and said centralconductor to support said conductor within said opening and in spacedrelation with respect to the inner walls of said opening; and acompressible medium having a relatively high thermal conductivity withrespect to the thermal conductivity of air being contained Within atleast a portion of the space defined by the external area of saidconductor and the internal area of the walls of said opening in saidinsulator housing; said medium comprising a conductive metal powder.

2. An electrical bushing insulator; said electrical bushing insulatorcomprising an outer insulator housing having a central opening therein,a conductor passing through said opening and extending beyond either endof said outer insulator housing and a support means; said support meansbeing connected between said insulator housing and said centralconductor to support said conductor within said opening and in spacedrelation with respect to the inner walls of said opening; and a mediumhaving a relatively high thermal conductivity with respect to thethermal conductivity of air being contained Within at least a portion ofthe space defined by the external area of said conductor and theinternal area of the walls of said opening in said insulator housing;said medium being comprised of a copper powder.

3. An electrical bushing insulator; said electrical bushing insulatorcomprising an outer insulator housing having a central opening therein,a conductor passing through said opening and extending beyond either endof said outer insulator housing and a support means; said support meansbeing connected between said insulator housing and said centralconductor to support said conductor within said opening and in spacedrelation with respect to the inner Walls of said opening; and a mediumhaving a relatively high thermal conductivity with respect to thethermal conductivity of air being contained within at least a portion ofthe space defined by the external area of said conductor and theinternal area of the Walls of said opening in said insulator housing;said medium comprising an electrically conductive material in particleform.

4. An electrical bushing insulator; said electrical bushing insulatorcomprising an outer insulator housing having a central opening therein,a conductor passing through said opening and extending beyond either endof said outer insulator housing and a support means; said support meansbeing connected between said insulator housing and said centralconductor to support said conductor within said opening and in spacedrelation with respect to the inner walls of said opening; and a mediumhaving a relatively high thermal conductivity with respect to thethermal conductivity of air being contained within at least a portion ofthe space defined by the external area of said conductor and theinternal area of the walls of said opening in said insulator housing;said medium being comprised of a copper powder; said insulator housingbeing of porcelain; the walls of said opening in said insulator housingbeing rendered conductive through said medium.

References Cited in the file of this patent UNITED STATES PATENTS1,079,352 Keyes Nov. 25, 1913 1,368,160 loutiret Feb. 8, 1921 1,703,409Smith Feb. 26, 1929 1,899,752 Estorff Feb. 28, 9133 2,318,922 CaringtonMay 11, 1943 2,351,964- Hill June 20, 1944 2,357,602 Peters et al Sept.5, 1944 FOREIGN PATENTS 605,512 France Feb. 19, 1926 OTHER REFERENCESDeinema, George R.: Bushing Modifications Reduce Corona, ElectricalWorld, June 2, 1952, page 104.

1. AN ELECTRICAL BUSHING INSULATOR; SAID ELECTRICAL BUSHING INSULATORCOMPRISING AN OUTER INSULATOR HOUSING HAVING A CENTRAL OPENING THEREIN,A CONDUCTOR PASSING THROUGH SAID OPENING AND EXTENDING BEYOND EITHER ENDOF SAID OUTER INSULATOR HOUSING AND A SUPPORT MEANS; SAID SUPPORT MEANSBEING CONNECTED BETWEEN SAID INSULATOR HOSUING AND SAID CENTRALCONDUCTOR TO SUPPORT SAID CONDUCTOR WITHIN SAID OPENING AND IN SPACEDRELATION WITH RESPECT TO THE INNER WALLS OF SAID OPENING; AND ACOMPRESSIBLE MEDIUM HAVING A RELATIVELY HIGH THERMAL CONDUCTIVITY WITHRESPECT TO THE THERMAL CONDUCTIVITY OF AIR BEING CONTAINED WITHIN ATLEAST A PORTION OF THE SPACE DEFINED BY THE EXTERNAL AREA OF SAIDCONDUCTOR AND THE INTERNAL AREA OF THE WALLS OF SAID OPENING IN SAIDINSULATOR HOUSING; SAID MEDIUM COMPRISING A CONDUCTIVE METAL POWDER.